Conventionally, for a type printer in which a transfer path for printing paper in the vicinity of a printing head is formed on the same flat surface, a flat-plate shaped platen has been used as a platen for performing printing on a paper by being subjected to an impact of a printing head. When such a flat-plate shaped platen is used, there is a problem in that the platen deteriorates early because the position subjected to the impact of the printing head is fixed.
Japanese Patent Publication No. 50-124724 has disclosed a technique such that a cylindrical platen is used in a type printing section provided at the lower part of the printer. However, since a mechanism for causing the cylindrical platen to rotate is not provided, the printing operation in this printing section is always performed at a fixed position of the platen. Also, Unexamined Japanese Patent Publication No. 57-152979 has disclosed a technique such that a substantially cylindrical platen is used in a type printer. However, this platen is formed with a flat surface at the upper part thereof, and this flat surface acts as a surface subjected to the impact of the printing head. Therefore, this platen is completely equal to the flat-plate platen in function.
Generally, a pressing roller of printer is disposed as a pair with a paper feed roller rotated by a rotation driving mechanism. Also, there is provided a pressing spring for pressing the pressing roller on the paper feed roller to rotate the pressing roller in a slave manner.
For a type printer having a continuous paper printing mode and a cut paper printing mode, usually, a cut paper is inserted from the front end of the printer, and a continuous paper is set on a tractor provided at the rear of the printer to be sent out to the front of the printer.
For the type printer, when work of removing a jamming printing paper or removing a printed head mounted on a carriage is performed, the work is difficult to perform because the pressing roller becomes a hindrance.
FIG. 30 is a plan view showing an arrangement of pressing rollers in a paper feeding device for a conventional printer. FIG. 31 is a sectional view taken along the line XXXI--XXXI of FIG. 30.
In FIGS. 30 and 31, reference numeral 51 denotes a printer, which has a pressing roller shaft 73a pivotally supported on side frames 52, pressing rollers 73 fixed coaxially to the pressing roller shaft 73a, a paper guide 71 for covering the transfer of a printing paper 60 so as to keep clear of the pressing rollers 73, and pressing springs 74 each of which is fixed to the paper guide 71 and the tip end of which presses the pressing roller shaft 73b on the side of a paper feed roller 75.
Also, a shaft hole of the side frame 52 on which the pressing rollers 73 are supported pivotally is open so that the pressing rollers can be moved vertically though not shown in the figure.
FIG. 31 shows a state in which the printing paper 60 is fed along a transfer path formed between the paper guide 71 and a transfer plate 59 while being held between the pressing roller 73 and the paper feed roller 75.
With the construction shown in FIGS. 30 and 31, since the printing paper 60 is covered by the paper guide 71, if jamming of the printing paper 60 occurs and part of the printing paper 60 remains, it is very difficult to remove the jamming paper.
Further, for the type printer having a continuous paper printing mode and a cut paper printing mode, a cut paper insertion section, the paper feed roller on the front side, the printing head, the paper feed roller and paper course switching section on the rear side, and the tractor are arranged in series to deliver the paper. Therefore, the depth of printer is increased undesirably.
Also, switching of paper course and a tractor drive transmission mechanism are needed to respond to the continuous paper printing mode and the cut paper printing mode, and the conventional mechanism is very complex.
Japanese Patent Application No. 8-239956 has realized the switching of paper course, the release of tractor drive transmission, and the vertical movement of paper feed roller by the use of a change plate having a complex shape though being a mechanism for driving a motor. However, a considerable distance is needed from the printing head to the position of tractor, so that the depth of printer is inevitably increased.
There have been proposed a various types of printers that can control a distance between the printing head and the platen, that is, the gap of printer head manually or electrically according to the thickness of paper used for printing.
Also, there is known the printer that can select continuous paper and cut paper as the paper used for printing, and can switch the paper course of continuous paper and cut paper manually or electrically.
In some of these printers, the gap control of printing head and the switching of paper course of continuous paper and cut paper are effected electrically. However, the electrical type is usually expensive and used for high-grade printers. On the other hand, since the gap control and the switching of paper course are effected infrequently, in some printers, the gap control and the switching of paper course are effected manually with the body configuration of printer being unchanged, by which the cost is decreased. However, some users who purchased a manual type printer often have a demand for remodeling the gap control mechanism or the paper course switching mechanism to an electrical type as necessary.
In order to meet the aforementioned demand, it is desirable that the manual type can be changed to the electrical type easily merely by installing an electrical power unit additionally. In this case, if the power unit installed for the gap control and the power unit installed for the switching of paper course are the same as a part, the same power unit can be used commonly for the gap control and the switching of paper course, which is preferable because the number of parts can be reduced, and the manufacturing cost and remodeling cost can be decreased.